BRCA1 and breast cancer: Conditional knock out of either Brca1 or Bard1 in murine mammary epithelial cells led to the development of mammary carcinomas that are indistinguishable from each other (Shakya et al., 2008), and the BRCA1 C61G mutant that abrogates BARD1 binding failed to suppress mammary tumor development in mice (Drost et al., 2011).